In JP 2010-236569 A, there is disclosed an example of the synchronization device for a manual transmission of a vehicle. This synchronization device includes a gear rotatable relative to a rotation shaft, a clutch hub rotatable integrally with the rotation shaft, a gear piece movable relative to the gear, and a synchronizer ring configured to couple a sleeve and the gear piece when the sleeve is moved in an axial direction. The synchronizer ring functions to synchronize the rotation of the gear and the rotation of the sleeve, to thereby couple the gear and the clutch hub so as to be rotatable integrally with each other.